Logic (yukti) is of two kinds: pure (suddha) and mixed (misra). Pure logic is present in the spirit soul in his original, pure nature. When the spirit soul is imprisoned in matter and his activities are mixed with material conceptions, then he possesses what I call mixed logic (misra-yukti). This mixed logic is of two kinds: mixed with fruitive action (karma-misra) and mixed with philosophical speculation (jnana- misra). This mixed logic is also known by the word "tarka" (material speculation). This mixed logic is very bad, for seen within it are the four defects: bhrama (mistakes), pramada (illusions), vipralipsa (cheating), and karanapatava (sensory inefficiency). The conclusions attained by this mixed logic are always faulty. Pure logic always arrives at the same conclusions. Mixed logic arrives at a great host of mutually contradictory conclusions. By acting according to the conclusions of mixed logic, the souls in the material world attain the result of being more and more stringently confined in the prison of the material world.
Logic, Matter and Reason
Mixed logic is born from matter. Looking through the door of the senses, the soul imprisoned in matter catches a glimpse of material images, a glimpse carried by the nerves to the brain. There the images are preserved by the power of memory. It is then that material logic does its work. In this way many ideas and imaginations are created. Sorting through these material images, material logic arranges them in pretty patterns. This is called science and philosophy. Looking this way and that at the sensory images, logic comes to certain conclusion. This is called reason. Comte says, "Carefully preserve and organize what you have seen. Examine that information to find the truth." By examining the images seen by the material senses, logic may understand something of the material world. Why should that logic not be called "material logic"? However, how can that material logic hope to understand the nature and activities that are beyond the material world? If something indeed exists beyond the material world, then a specific process to understand it must certainly also exist. If, unaware of that spiritual process of obtaining knowledge, and not wishing to understand whether such a process exists, an uneducated barbarian takes shelter of material logic alone, then that person will talk only nonsense. How can there be any doubt of that?
Only when it is directed towards understanding the workings of the material world does that material logic bring any good results. For engineering, medicine, warfare, music, and other like material activities mixed logic is very suitable. First is material logic mixed with philosophical speculation (jnana-misra yukti). In this, the theoretical stage, the scientist understands general principles. After that comes the second stage, where the theoretical knowledge is applied to solving practical problems. This is called karma-misra yukti. For example, in building a railroad, first comes the theoretical stage (jnana-misra yukti), and then the stage of application (karma-misra yukti), where the railroad is actually built.
Engineering and other like activities are the proper sphere of mixed logic. The world beyond matter is not the proper sphere of mixed logic. Mixed logic cannot understand that world. Only spiritual logic can understand the world beyond matter. Materialism, the worship of material nature, the philosophy of the cessation of existence (nirvana), and Skepticism take shelter of material logic to understand the original cause of the material world, a cause that is beyond matter. Using material logic for this purpose will never bring a happy result. That is why these philosophies have become the object of laughter. Whatever books these philosophers have written are only nonsense chattering.
Spiritual Logic - the Logic that is Beyond Matter
Pure spiritual logic is the natural endowment of the soul. Still, when he is imprisoned in the world of matter, the soul, always meditating on matter, thinks mixed logic is better. In this way most of the people in this world are followers of mixed logic. It is rare in this world to find a follower of pure logic, the logic that is beyond matter. Only those fortunate souls who know the secrets of service to God appreciate pure spiritual logic, for they know the glories of rapt meditation (samadhi) on God. For a long time the people of this external material world have, hoping in this way to fulfill their selfish desires, honored mixed logic. They gave great honor to the ideas material logic gave, but in the end the people could find no happiness. This material, or mixed logic will not leave the soul.
Sometimes material logic tries to help the soul. Arguing for a great variety of philosophies, as speaking in many different ways, mixed logic did not become happy. Then material logic began to hate itself. Talking and talking, material logic wept and lamented. It said, "Alas! For how long have I labored in this external material world? I have fallen very far away from the soul, my eternal companion. I have rejected my own true nature." Lamenting and lamenting in this way, and now filled with fears, at the end material logic accepts God as the original cause of all causes. In country after country is found this kind of preaching about God, preaching born from the human mind and from material logic. Udayana Acarya described this idea in his book Kusumanjali. In Europe and the West this kind of dry belief in God, called "Deism" or "Natural Theology", has come from many minds. There it has a certain popularity. When it is thus established by mixed logic, knowledge of God is very incomplete and imperfect. That is because material logic is very weak and unqualified to bring the soul closer to God. Because it is thus against its own nature, material logic cannot elevate the soul. Material logic cannot bring spiritual knowledge or guide the soul. This will be shown later in this book .
Material Logic – Logic Bewildered by Matter
Mixed logic may sometimes accept the existence of God. Still, bewildered by matter and always talking nonsense, mixed logic has no power to accept that there is only one God. Sometimes mixed logic thinks there are two Gods. Then it thinks there is a God of spirit and a separate God of matter. The God of spirit brings auspiciousness, and the God of matter brings troubles. A philosopher named Zarathustra (Zoroaster) taught this idea: That there is a God of spirit and a God of matter. In his book Zend-Avesta he taught that these two Gods are eternal. The devotees of God have only contempt for these old speculations. In the same way they also have contempt for the atheistic jnana-kanda (philosophy of speculative knowledge) and karma-kanda (philosophy of fruitive work).
Zarathustra is a very ancient philosopher. When his philosophy found no honor in India, Zarathustra preached it in Iran. It was by the influence of Zarathustra's ideas that Satan, an equally-powerful rival to God, made his imaginary appearance first in the religion of the Jews and then in the religion based on the Koran. Then, influenced by Zarathustra's idea of two Gods, the idea of three gods, or a "Trinity" made its appearance in the religion that had come from the Jewish religion. At first they were considered three Gods, but then, when the philosophers were displeased with that idea, the Trinity became God, the Holy Ghost, and Christ. At the same time, in India, Brahma, Visnu, and Siva came to be considered three different competing Gods: a very foolish idea. Some philosophers then preached that these three are actually only one God, and indeed many passages of the Vedic scriptures forbid us to think of them as three separate, independent rival Gods. In many other countries is seen faith in many different Gods simultaneously.
Indeed, among the countries with the lowest level of civilization it is difficult to find pure belief in one God. Sometimes Indra, Candra, Vayu, and others are considered independent rival Gods. Different philosophers refuted that mistaken idea and proved that Brahman alone is God. These ideas of many Gods are only the foolish babbling of ordinary logic bewildered by matter. There is only one God. If there were more than one God this material world would not be organized so well. If there were many competing independent Gods, they would decree different, conflicting material laws, each according to his own desire. Of this there is no doubt. Looking at the material world, an intelligent and thoughtful person cannot fail to accept the idea that it was created according to the will of a single Supreme Person.
The Natural Knowledge of the Soul – Axiom of the Spiritual Science
Logic that comes from the soul's own natural knowledge is pure and faultless. The philosophy that comes from such logic is the actual truth. Separated from that natural knowledge, true logic has no power to stand. However, logic that comes from material knowledge, the logic that is seen everywhere in this world, is always mixed and impure. Philosophies that come from such mixed logic are always faulty and lacking. Such philosophies are never good at describing God. Mixed logic is not the proper tool to describe the Supreme Truth. Pure logic which takes shelter of the soul's natural knowledge is the proper tool to describe the Supreme Truth. Here someone may ask, "What is this natural knowledge of which you speak?" The answer is: The soul is spiritual, and therefore naturally full of spiritual knowledge. That original knowledge possessed by the soul is called here "natural knowledge". That natural knowledge is eternally present in the soul. It is not created by perceiving the contents of the material world. The activities of that natural knowledge are called pure logic. That natural knowledge was known by the soul before the soul ever had any knowledge of the material world.
That knowledge is: (I) I am. (2) I continue to be. (3) I am happy. (4) My happiness comes from a certain place: a shelter, a reservoir of happiness. (5) It is natural for me to take shelter of that reservoir of happiness. (6) I am eternally a follower of that reservoir of happiness. (7) That reservoir of happiness is very beautiful. (8) I have no power to abandon that reservoir of happiness. (9) My present condition is lamentable. (10) Abandoning that lamentable condition I should take shelter of that reservoir of happiness. (11) This material world is not my eternal home. (12) By becoming elevated in this material world I do not become elevated eternally.
If logic does not take shelter of this natural knowledge, logic remains mixed with matter. Then logic is only a babbler of nonsense. Even in ordinary material science, first some axioms must be accepted. In mathematics, astronomy, or other sciences, one cannot make progress if one does not first accept the axioms. In the science of understanding the Supreme Truth one must also first accept some axioms, the axioms given by natural knowledge. Those axioms are the root from which the tree of spiritual knowledge grows.
Excerpted from the “Tattva-viveka” of Srila Bhaktivinoda Thakura, Commentary on verses 18-22